Yard hydrants have long been employed to dispense water supplied by underground water pipes at various locations where needed. For the most part, these hydrants can be relatively simple and inexpensive, yet provide reliable service over extended time periods. A problem arises, however, in areas where below-freezing temperatures are encountered because the valve pipes and control valves are commonly located at or a few feet above ground level and thus are fully exposed to outside temperatures. When water in a control valve or water pipe freezes, the expansion of the water in its frozen state often causes damage to a control valve or pipe. Thereafter, when the frozen water thaws, the water uncontrollably escapes, thereby creating the possibility of water damage, besides the loss of valuable water supply.
In some applications, it is possible to merely shut off the water pressure source to the hydrant when there is a chance of freezing temperatures and to drain down the exposed portion of the water line above ground and a distance below the surface of the ground to a depth below the frost line for a particular geographic area. In many other applications, it is not possible to merely shut down the hydrant in this manner during potentially freezing weather conditions due to the necessity to have it continually operable for purposes of watering livestock or the like.
In some instances, electrical heating elements have been employed to prevent water in hydrants from freezing. However, such heating devices are relatively expensive, require substantial work and expense to install and maintain, and tend to consume substantial electrical power in employing relatively inefficient electrical resistance units. In addition, there are a vast number of locations where hydrants are installed that electrical power is not readily available. Further, a loss of electrical power, even for a short time period, can result in the water freezing and the attendant damage to the pipe and/or control valve.
The other approach that has been emplpoyed to prevent freezing besides permanent shutdown or the use of a heat source to maintain the water above freezing involves systems that effect a temporary drain down any time that water flow is discontinued. Some such systems employ a stop cock position led below the freezing line with provision for draining the water from the vertical pipe between the stop cock and the above-ground control valve. In some instances, this is effected by employing a small weep hole in the vertical pipe below ground and normally proximate to the below-ground stop cock. Such weep holes are normally on the order of one-sixteenth of an inch in diameter to permit the water to drain into the ground. Systems of this type do have disadvantages. First, it is possible for contaminated water in the ground to enter the weep hole and contaminate the water when the stop cock is opened and water flow to the control valve is resumed. A common source of such contaminated water arises from usage of a spray nozzle for dispensing insecticides and fertilizers where back flow through the weep hole may result and the water source may be thus contaminated. Another problem with the weep hole approach is that rust may readily form at the weep hole after a period of time and result in blockage of the weep hole. In such instance, the water is unable to drain down, which, upon the occurrence of freezing temperatures can result in damage and breaking of the vertical pipe and/or the control valve.
Another type of temporary drain-down system contemplates connecting the vertical pipe to a tank, which permits water in the vertical pipe to drain down into the tank. In such systems, a venturi is positioned in the line, such that the tank is pumped out when water flow is resumed so that it is then ready to receive drain-down water when water flow is again discontinued. While this system is a closed system that does not permit discharge of water into the ground or possible return flow of contaminated ground water, there is nevertheless a build-up of bacteria in the tank that is expelled when water flow is resumed, particularly when the hydrant stands for substantial time periods without being actuated to clear the tank.
Thus, all known systems for preventing freezing of yard hydrants and the like are subject to limitations and disadvantages that can result in either the water becoming contaminated or in freezing of the water under circumstances that are likely to intermittently occur.